This invention is an improvement to a flying disc which returns to the user by means of a string or corresponding elongated part, and uses rotational energy for the return flight in a way that resembles yo-yo motion. It may be used as a toy, for recreational purposes and as sporting equipment.
The device known as a yo-yo exemplifies some of the existing technology that precedes the present invention. A yo-yo returns to the user by means of a string that first winds out and then in around an axle. The string forces the falling yo-yo to rotate and the primary source of this rotational energy is gravitational potential energy that is converted into rotational kinetic energy. The essential directions of its basic translational motion are vertical. It does not glide supported by air. Due to these characteristics the length of the yo-yo string is about 0.5-1 metre.
A traditional saucer-shaped flying disc is represented, for example, in U.S. Pat. No. 3,359,678, Headrick et al. This device rotates around its upright axis during translational flight generating lift. A great number of different forms of flying disc have been developed from the basic idea and many of these have been patented. It is appropriate to refer here to a ring-shaped flying disc represented, for example, in U.S. Pat. No. 4,560,358, and consisting of a ring-shaped airfoil with an uncovered inner area. These ring-shaped flying discs are somewhat more closely related to this invention than the traditional discs, in that the solutions to the problems of realising proper aerodynamic lift and low air-resistance are somewhat similar to the present invention. The traditional flying disc and its further developed versions are usually used by several people, who throw the disc to one another. Otherwise the lone user has to follow the disc and retrieve it each time after it has landed.
Goals and problems that somewhat more closely resemble those of the present invention, are sought and resolved in U.S. Pat. No. 3,802,117 by Engelhardt, and in patent publication WO 92/11913 by Tomberlin. A device according to Engelhardt""s patent in its basic form consists a saucer-shaped flying disc, beneath which is a reel attached to a string. The user end of the string is fastened to a wand. The purpose of the device is to reel back to the person using it by means of the string. As the reel is positioned beneath the device and at a distance that is relatively remote from its centre of gravity, the device tends to dive or climb at steep angles when the string tightens during flight and the flight then fails. For this reason it is difficult to make the device rotate and move fast enough. The solution proposed in the publication for achieving flight stability is an additional weight added to the lower end of the reel, but this added weight actually creates new problems. A flying toy according to Tomberlin""s publication has two identical rotary elements joined by an axle. The rotary elements are furnished with wings that create lift when the device rotates. This device creates lift expressly and exclusively by this rotary motion around its vertical axis. After each cast it has to be turned upside down so that the airfoil-wings are in a position to generate lift.
While the devices here described attempt at least partially to solve the same problems, they differ considerably from the present invention in respect of their solutions. A type of flying disc that is more of a starting point for the present invention and its improvements is represented in Finnish patent no. 93426, throw and fly device by Kaisio and Kukkonen. A flying disc according to this patent consists of a convexo-concave base-part resembling a traditional flying disc with a top-mounted flange at the end of a short axle. There is a space for the string between the flange and the base-part. This space is about as wide as the diameter of the string. The device flies supported by air and rotates around its vertical axis. The energy conserved in rotary motion returns the device to its user by means of a string in a way that resembles the function of the yo-yo.
An important problem of devices configured according to Pat. No. 93426 FI is caused by this very narrow space for the string, which is only the diameter of the string or at most 1-2 diameters. This leads to a situation where the length of string for a single winding around the axle changes considerably during flight. This means that the angular momentum of the device decreases as it approaches its user. At the same time kinetic energy of rotation is also consumed in correcting the flight path and in overcoming air-resistance. The flight speed therefore decreases and there is a practical problem that flight often stalls before the return is complete. Another trouble is that the string tends to tangle into the proposed narrow space in a way that is often difficult to disentangle and quite frustrating to the user.
Considerable improvements are achieved by a flying disc configured according to the present invention. In particular, the air-resistance is lower and the aerodynamic properties are more favourable than those of Pat. no. 93426 FI and other predecessors. The invention is based on the fact that air-currents flowing over and under the translationally moving circular airfoil that forms part of this yo-yo returning flying disc, are able to mix through openings in the area bounded by the inner edge of the circular airfoil and the axle. The present invention constitutes a breakthrough for more balanced flight and lower air-resistance. These have hitherto remained major problems in all known solutions for flying discs employing some kind of string arrangement and yo-yo function. There are also other benefits.
A yo-yo returning flying disc configured according to the present invention can be constructed to be lighter in proportion to the aerodynamic lift which it generates. This enables it to glide at lower translational speeds. It returns more easily than its predecessors on longer strings. The improved flight properties also make it easier for a beginner to fly the device with a relatively short string. Improved aerodynamic properties also make its flight more stable in windy conditions.
Using a slinging technique and a lighter construction according to the present invention the flying disc may be accelerated to a considerably faster rate of rotation. In this rotation the kinetic energy increases in direct proportion to the square of the speed. It may thus be considered capable of storing more energy in the form of rotational movement than earlier versions. This increased rotational kinetic energy provides enhanced stability at the turning point where the string tugs on the flying disc and it reverses its direction of flight. The location of the string vertically close to the centre of gravity also favourably influences stability of the flying disc at this turning point.
One further benefit of the lighter construction is that the impact of the flying disc is reduced in the event that it accidentally collides with the user. The user may be relaxed about flying the device and need not worry about being hit by some rapidly flying heavy object if he fails to catch it.
Compared to current technology a construction according to the present invention brings about these and certain other improvements. The present invention is characterised by the claims appended hereto.